Filters are used in a wide range of applications to remove contaminant material from a fluid flow. Often the accumulation of the contaminant material on the filter media negatively impacts the operation of the overall filtration system, through a restriction in flow through the filter and increased backpressure.
Over time particulate matter builds up in the filter. The particulate matter is composed of soot, defined as the combustible fraction which includes carbon, sulfates, and organic matter. Aside from the combustible fraction, the particulate matter also contains incombustible material or ash. The ash, generally composed of metal oxides, sulfates, and phosphates, may originate from lubricant additives, engine wear metals, trace metals in diesel fuels, and many other sources. While the combustible fraction of the particulate matter may be removed from the filter during regeneration, through oxidation, the incombustible material or ash remains.
Following extended use, the ash plugs the filter channels. The ash may accumulate on the filter walls, in an end plug at the back of the channel, in the filter pores, or some combination of these locations. The ash plugging restricts flow through the filter and leads to increased exhaust backpressure, which negatively impacts vehicle fuel economy. The ash also occupies a significant portion of the filter volume, reducing its soot storage capacity, and thus requiring more frequent filter regeneration. More frequent filter regeneration also leads to increased fuel consumption. Further, ash may also degrade the performance of catalysts used in these filter systems, and interact with the filter material itself, such as through sintering, pitting, and other means, which also degrades the integrity of the filter. The ash, thus, is one of the most important parameters limiting the service life of the filter. Once significant amounts of ash have accumulated in the filter, and its performance has degraded below a certain level, the filter must be removed for ash cleaning or replacement.
In order to mitigate the ash problem, larger filters may be used (over-sized) to provide additional storage space to accommodate the build-up of ash over time. The use of larger components incurs added costs, and takes up valuable space which could be used for other purposes.
The spatial distribution of the ash, as well as the physical ash properties, particle size, packing density, porosity, permeability, and the like are the most important parameters controlling the magnitude of the ash impact on the particulate filter. Therefore, a system and method for manipulating the ash properties and spatial distribution by varying the operation of the engine and aftertreatment system in a specific manner, would be beneficial.